Last year’s fatal East Side crane collapse could have been prevented had the rigger in charge replaced some old, worn-out polyester straps with new ones costing just $50 each, an outraged Manhattan DA said yesterday in announcing the rigger has been charged with homicide.

William Rapetti had been offered eight new straps – called “slings” – to use on the crane tower only moments before the collapse, but turned them down and proceeded with the old slings, DA Robert Morgenthau said, calling the alleged corner-cutting “shocking” and “outrageous.”

“The construction manager had new slings available and offered them to Rapetti, but Rapetti rejected them,” Morgenthau said in a press conference revealing that the crane rigger – owner of Rapetti Rigging Services – and his company have been charged with seven counts each of homicide and manslaughter, one for each death caused by the March 15 collapse at 303 E. 51st St.

“A sling costs $50, but Rapetti was willing to risk these lives by failing to use new slings,” the DA said of the straps used to hold aloft a 5-ton steel collar that was to be used to attach a new, higher section of crane to the construction project.

“I find that the most shocking fact in this entire case.”

Morgenthau said an investigation led by his office and the city Department of Investigation revealed multiple errors in the hoisting of the steel crane tower to the building’s 18th floor, the height at which the polyester slings snapped, causing the collapse.

Rapetti used four slings, instead of eight required by city and federal regulations, and one of the slings had obvious pre-existing damage, the DA said.

Rigging crew members also wrapped the slings around sharp edges on the collar without any protective padding to prevent them from being shorn, Morgenthau said.

Rapetti, 48, of Massapequa Park, LI, faces up to 15 years in prison if convicted. He pleaded not guilty at his arraignment yesterday, and was released on $75,000 bail.

Arthur Aidala, a lawyer for Rapetti, said his client followed all the proper procedures, insisting that each strap can handle 25,000 pounds of weight and that regulations call for the use of only four.

The lawyer said Rapetti has been in the construction business for 30 years, without a single violation, and served tirelessly as a crane operator at Ground Zero.

“His record is clean as a whistle,” Aidala said. “Billy Rapetti would not look at a strap that was slightly worn and use it.”

Aidala said Rapetti was close friends with five of the victims. “The guilt that he feels is the guilt that he didn’t die himself,” the lawyer said.

The crane collapse was one of two last year.

Two workers were killed in May in the collapse of a crane on East 91st Street, which remains under investigation by Morgenthau’s office and the DOI.